As is well known in the aeronautical field of technology the fuel pumping systems for turbine types of power plants are relatively complex owing to the fact that the pumping system must meet the demands of fuel flow for every engine operation. Of all the types of fuel pumping systems, perhaps, the most efficacious pumping system from a standpoint of cost effectiveness and reliability is the positive displacement types, i.e. gears, vanes or pistons, that utilize a valve to by-pass excess fuel.
However, one of the major problems associated with the pumping system is the high temperature rise in the fuel occasioned by by-passing excess fuel during certain engine operations. Hence, from idle which is at the low demand of the spectrum to take-off which in commercial aviation is at the high demand of the spectrum the fuel pumping system must almost instantly supply the volume of fuel at the proper pressure levels from a low fuel flow to a high fuel flow. Of necessity, the fuel pumping system will continually by-pass a certain percentage of the total fuel being pumped and return this excess fuel to the pump's inlet.
Obviously, the by-pass flow that recirculates through the pump continues to extract heat from the pumping operation with a consequential rise in fuel temperature contributing to the constraints of the pumping system's hardware.
Obviously, any system that can reduce fuel temperature during this operating condition would immensely contribute to the efficacy of the overall fuel system. For example, in gas turbine power plants the utilization of this invention would not only eliminate the complex and heavy mechanism that is customarily used to vary the geometry of the pump or the piston stroke, but it also would eliminate the customary use of the complex by-pass valve and the complex control system. As will be appreciated from the description to follow and in accordance with this invention the control of the pumping system is inherent thereby eliminating the complexity associated with the control system.
It is contemplated within the scope of this invention, that when employed in a gas turbine engine, this invention will be made compatible with existing fuel control systems. Examples of such systems are the full authority digital electronic control system (FADEC), the supervisory control system or the hydromechanical fuel control systems. Obviously, FADEC systems utilize electrohydromechanical valves which differ from those utilized in other types of systems. However, this invention can still be employed with substitute types of flow control apparatus. It will be appreciated that from the discussion to follow that this inventive concept can be adapted to most, if not all, new and proposed fuel or engine control systems for gas turbine engines that provide a signal indicative of the amount of fuel being demanded.
As an integral part of a fuel system for a gas turbine engine, whether powering aircraft or other vehicles or used as an industrial application this inventive system will control the fuel flow to the engine from a maximum to minimum fuel flow ratio of say, 37 to 1, without incurring excessive rise in the temperature of the fuel. As will be discussed in more detail hereinbelow this invention also inherently eliminates the necessity for fuel metering valves and/or flow meters inasmuch as this invention can be readily and easily adapted to calculate the fuel flow since it can be easily synthesized merely by measuring pump speed and fuel temperature.
Another important aspect of this invention is that it affords the ability to readily and easily monitor the health of the engine's pumping system and the amount of fuel being delivered to the engine. As will be evident from the description to follow, the pumping operating parameters are readily available and can easily be computed and lend themselves to be indicative of certain conditions of the pump.
While in its preferred embodiment, this invention is being contemplated for use in the field of aeronautics, as one skilled in this art will appreciate, this invention has utility in any positive displacement pumping system that requires by-passing fluid during the low power regime of the operating envelope. For example, it is contemplated within the scope of this invention that it can be utilized in a fluid drive system for say automobiles that use a pumping system to propel the vehicle by driving the automobile's wheel with a hydraulic motor. In this instance, the positive displacement pumps would generate the pressure and flow to drive the hydraulic motors that would be operatively connected to the wheel.
By way of illustration and without limitation another application where this invention has utility is in heavy equipment, as cranes, jacks, lifts, hydraulic elevators and the like which require large actuators.
This invention contemplates utilizing a planetary gearing system that uses the auxiliary drive of the engine to drive the sun gear which, in turn, drives the ring gear for driving one of the positive displacement pumps and the cage of the planetary gears for driving the other pump. By proper and judicial sizing of the positive displacement pumps which may be, for example, gear pumps and its judicious fluid flow circuitry interconnecting the EHV or other suitable flow control apparatus and the engine's combustor, fuel flow is properly metered on demand while the pumping system adjusts its pressure and flow requirements during the low power operations of the operating envelope to avoid the high fuel temperature rise which other wise would occur.